1. Field of the Invention
The present invention relates to a fixing member such as a roller, a sheet, an endless belt, or the like, which is used for an image forming apparatuses such as an electro-photography copying machine, a laser printer, a facsimile, and so on, and the image forming apparatus, which comprises the fixing member.
2. Description of the Prior Art
FIG. 3 is an explanatory view showing an image forming apparatus of a conventional electro-photography type. In the image forming apparatus of the conventional electro-photography type 100, for example, a copying machine and a laser printer have a photoconductor drum 101 in which an electrostatic latent image is formed on a surface, an electrification roller 102 in which an electrification treatment is conducted by contacting to the photoconductor drum 101, exposure means 103 such as a laser beam, and so on, a development roller 104 in which a toner is adhered to the electrostatic latent image formed on the photoconductor drum 101, a power-pack 105 in which a DC voltage is applied on the electrification roller 102, a transfer roller 106 in which a toner image formed on the photoconductor drum 101 is copied on a detail paper 107, a cleaning device 108 in which the photoconductor drum 101 of after transfer treatment is cleaned, a surface electrometer 109 in which an electro potential of the surface of the photoconductor drum 101 is measured, and a thermal fixing device of roller process 110 composing of a thermal fixing roller 111 and a pressurization roller 112.
In this conventional image forming apparatus 100, the electrostatic latent image is formed by exposing with the exposure means 103 after equally charged by the electrification roller 102 on a photoconductor layer on the surface of the rotated photoconductor drum 101. A toner image is created by a development of this electrostatic latent image adhered the toner thereto. Then this toner image is transferred to the detail paper 107. Moreover, the toner image is thermal fixed in such a manner that the detail paper 107 in which the toner image is transferred is passed through the thermal fixing device 110 of roller process composing of the heat fixing roller 111 and the pressurization roller 112.
In the thermal fixing device 110, the heat-fixing roller 111 is used. The heat fixing roller 111 is provided with a releasing layer composing of fluorocarbon resin such as tetrafluoroethylene resin (PTFE), tetrafluoroethylene perfluoroalklvinyleter copolymer resin (PFA), tetrafluoroethylene hexafluoropropylene copolymer resin (FEP), and so on, which are coated in order to prevent adhesion of the toner to a peripheral surface of a core formed from a hollow cylinder of a metal such as aluminum, and so on. The releasing layer is provided to separate the toner from the roller.
In the heat-fixing roller 111, a hollow portion of the core is provided with a heater such as a halogen lump, and so on along a line of a rotation center. The heat-fixing roller 111 is heated from an inside by radiant heat. When the detail paper 107 is passed through between the heat fixing roller 111 and the pressurization roller 112, the toner, which is adhered to the detail paper 107, is fixed on the detail paper 107 in such a manner that the toner is soften and pressured by the heat of the heat fixing roller 111.
Four colors of toners such as red (magenta), blue (cyan), yellow (yellow), and black (black) are used for the conventional image forming apparatuses such as a full color copying machine, the laser printer, and so on, and these colors of toners are overlapped, and then transferred on a paper.
Consequently, when an unfixed color toner layer is fixed, it is necessary for each toner layer to be developed colors as a transparency condition by melting. Sufficient melting of the toner is necessary for improving a transparency performance of an OHP film. When a surface of the toner layer is roughed, the transparency performance of the OHP film is declined with declining glossiness. Therefore the surface of the toner layer is required to be smoothed. Moreover, if the unfixed toner layer causes a misalignment and so on at the time of fixing, the image becomes unclear. Therefore, the toner layer should be flexibly and equally pressed on the paper and equally fixed by the fixing member. As mentioned above, the color toner is adapted to generate a sharp-melt property of material by lowering a softening temperature and the transparency performance of the OHP film so that an offset is easy to be generated by adhering to the surface of the fixing member. Consequently, beside heat-resistance, special characteristics such as flexibility, the releasability of the fixing member from the toner, endurance, and so on are required for the fixing member.
However, the heat fixing roller in which the core (i.e. a substrate) is provided with a layer of fluorocarbon resin is advantageous for the releasability, but it is disadvantageous for the flexibility, elasticity, and so on. Therefore the heat fixing roller can not correspond to the image forming apparatus such as the full-color copying machine, a full-color laser printer, and so on.
In order to provide the flexibility on the surface layer of this thermal fixing roller, a heat fixing roller in which the core is provided with an elastic layer composing of heat-resistance synthetic rubber such as silicone rubber, fluorine-contained rubber, or the like is proposed.
Provided the elastic layer on the core in this way, the equal fixing for a black-and-white image can be accomplished. Moreover, in case of a full-color image, it is possible for a plurality of the color toners to be melted and mixed equally so that various characteristics of an image quality such as the glossiness and the fixing are improved.
A method of fixing the thermal roller is capable of maintaining a whole heat roller at predetermined temperature, and also it is suitable for speeding up of a printing speed due to a large heat capacity of the heat roller. However, there were problems such that a considerable time to heat the heat roller till predetermined time is required and also an electric power consumption to heat the whole heat roller is increased.
Consequently, an effort for saving of energy is encouraged recently, and shortening of a rising time is considered. As a measure for that, a belt type fixing device to heat the toner on the detail paper through a film typed endless belt heated by the heater is proposed.
FIG. 4 is an explanation view for a conventional fixing device of belt type. As shown in FIG. 4, the image forming apparatus of conventional electro-photography process comprises a fixing belt 113 rotatably provided by a heat roller 115 and a fixing roller 114, and also a belt type thermal fixing device 117, which comprises a pressurization roller 116 provided as contacting to the fixing roller 114 through this fixing belt 113.
In this belt type thermal fixing device 117, the detail paper 107 is passed through between the fixing belt 113 heated by the heat roller 115 and the pressurization roller 116, and then the toner adhered to the detail paper 107 is fixed on the detail paper in such a manner that the toner is softened by the heat of the fixing belt 113 and is pressured by the pressurization roller 116.
In this belt type thermal fixing device 117, the thin film typed fixing belt 113 is directly heated so that the heated portion reaches to the predetermined time in short time after power is applied. Therefore a waiting time after the power is applied can be reduced. Moreover, it is advantageous in that only required portion is heated so that the electric power consumption is small.
Conventionally, in this kind of the fixing belt 113, a belt in which an elastic layer (not shown) composed of the rubber is formed on a surface of a substrate (not shown) has been adopted. For the fixing belt 113, a method for impregnating the surface with the silicone oil for the releasablity has been adapted.
However this method includes problems as follows;    {circle around (1)} a user maintenance such as a replenishment of the silicon oil is required.    {circle around (2)} a cost is increased by attaching a system of the replenishment of the silicone oil.    {circle around (3)} a the silicone oil is adhered to the transfer paper so that a pen is not able to be used to write on the transfer paper.According to the above-mentioned problems, a fixing belt, which does not use the silicone oil, is required.
Therefore, as the fixing belt, which does not use the silicone oil, a composition of the fixing belt in which the releasing layer is formed on the surface of the elastic layer of the above-mentioned fixing belt, is proposed. As materials to compose this releasing layer, fluorocarbon resin such as tetrafluoroehylene resin (PTFE), tetrafluoroehylene-perfluoroalkylvinyleter copolymer resin (PFA), tetrafluoroethylene-hexafluoropropulene copolymer resin (FEP), and so on have been used.
As described above, there are many kinds of the fixing materials such as the fixing roller and the fixing belt in which the releasing layer on the surface of the elastic layer is provided; however, some of these fixing members include a formation of the releasing layer in such a manner that the surface of the substrate is coated with the heat-resistance synthetic rubber such as silicon rubber to form the elastic layer, and then the surface of the elastic layer is coated with fluorocarbon resin of dispersion liquid (drainage texture dispersion paint) or powdered paint, then the releasing layer is formed by heating baking this paint above a melting point to form a film.
However, the melting point of the fluorocarbon resin, which composes the aforementioned releasing layer, is 327° C. for PTFE, 310° C. for PFA, and 275° C. for FEP. These are high temperature. Therefore, for the conventional fixing roller and the fixing belt, when the releasing layer is formed by baking the fluorocarbon resin with above-mentioned high temperature, depending on a combination with the heat-resistance synthetic rubber composing the inside layer of the elastic layer of the releasing layer, there is a problem of generating a crack on the elastic layer by oxidizing and deteriorating this heat-resistance synthetic rubber.
When the crack is generated on the elastic layer as this, there were problems that a surface quality of the fixing member is lost, and the toner is remained in a part of the crack generated on the surface of the fixing member, and as a result, defects such as an image fixing fault, and so on are generated by a stained image and an unevenness of a surface. When loads such as jamming of the transfer paper, a contact of a removed pawl, and so on are imposed, only the releasing layer is peeled so that the melted toner is not able to be released. As a result, there is a problem that the transfer paper is wound around the fixing roller.
In order to avoid the problems of the surfaces of these fixing members, recently, for example, as shown in Japanese Patent Laid-Open Hei 10-148988, a fixing roller that after the core; i.e. the substrate is inserted into a tube of fluorocarbon resin, the fixing roller is formed by casting the heat-resistance synthetic rubber such as the silicone rubber and so on into between the tube of fluorocarbon resin and the substrate is proposed. In this fixing roller, the tube of fluorocarbon resin is created separately so that it is not necessary to higher the temperature of the heat-resistance synthetic rubber constituting the elastic layer, and it is advantageous in that the deterioration of the heat-resistance synthetic rubber can be prevented.
However, there is a limit for thinning a film for the tube of fluorocarbon resin. Therefore, the fixing roller produced by this method becomes a hard fluorocarbon resin layer of a thick film, and the flexibility of required characteristic is lost, and problems such as generating unevenness of brilliance on the toner surface and unevenness of image on the OHP are caused.